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          <h1 class="post-title" itemprop="name headline">详解JavaScript继承的几种方式</h1>
        

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        <h3 id="属性拷贝"><a href="#属性拷贝" class="headerlink" title="属性拷贝"></a>属性拷贝</h3><blockquote>
<p>就是将对象的成员复制一份给需要继承的对象</p>
</blockquote>
<a id="more"></a>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 创建父对象</span></span><br><span class="line"><span class="keyword">var</span> superObj = &#123;</span><br><span class="line">  name: <span class="string">'Li'</span>,</span><br><span class="line">  age: <span class="number">25</span>,</span><br><span class="line">  friends: [<span class="string">'小明'</span>, <span class="string">'小李'</span>, <span class="string">'小赵'</span>],</span><br><span class="line">  showName: <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    alert(<span class="keyword">this</span>.name);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">// 创建需要继承的子对象</span></span><br><span class="line"><span class="keyword">var</span> subObj = &#123;&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">// 开始拷贝属性(使用for...in...循环)</span></span><br><span class="line"><span class="keyword">for</span>( <span class="keyword">var</span> i <span class="keyword">in</span> superObj )&#123;</span><br><span class="line">  subObj[i] = superObj[i];</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(subObj)</span><br><span class="line"><span class="built_in">console</span>.log(superObj)</span><br></pre></td></tr></table></figure>

<p><strong>存在问题：</strong></p>
<blockquote>
<p>如果继承过来的成员是引用类型的话,<br>那么这个引用类型的成员在父对象和子对象之间是共享的,<br>也就是说修改了之后, 父子对象都会受到影响.</p>
</blockquote>
<h3 id="原型链继承"><a href="#原型链继承" class="headerlink" title="原型链继承"></a>原型链继承</h3><blockquote>
<p> 将父类的实例作为子类的原型</p>
</blockquote>
<p><strong>父类：</strong></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 定义一个动物类</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Animal</span> (<span class="params">name</span>) </span>&#123;</span><br><span class="line">  <span class="comment">// 属性</span></span><br><span class="line">  <span class="keyword">this</span>.name = name || <span class="string">'Animal'</span>;</span><br><span class="line">  <span class="comment">// 实例方法</span></span><br><span class="line">  <span class="keyword">this</span>.sleep = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在睡觉！'</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 原型方法</span></span><br><span class="line">Animal.prototype.eat = <span class="function"><span class="keyword">function</span>(<span class="params">food</span>) </span>&#123;</span><br><span class="line">  <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在吃：'</span> + food);</span><br></pre></td></tr></table></figure>

<p><strong>子类：</strong></p>
<figure class="highlight stata"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">function <span class="keyword">Cat</span>() &#123;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">cat</span>.prototype = new Animal()</span><br><span class="line"><span class="keyword">cat</span>.prototype.name = <span class="string">"cat"</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">var</span> <span class="keyword">cat</span> = new <span class="keyword">Cat</span>();</span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span>.name)</span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span>.eat('fish'))</span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span>.<span class="keyword">sleep</span>())</span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span> instanceof Animal)  <span class="comment">// true</span></span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span> instanceof <span class="keyword">Cat</span>) <span class="comment">// true</span></span><br></pre></td></tr></table></figure>

<p><strong>特点：</strong></p>
<blockquote>
<p>1.纯粹的继承关系，实例是子类的实例，也是父类的实例<br>    2.父类新增原型方法/原型属性，子类都能访问到<br>    3.简单，易于实现</p>
</blockquote>
<p><strong>缺点：</strong></p>
<blockquote>
<p>1.可以在Cat构造函数中，为Cat实例增加实例属性。如果要新增原型属性和方法，则                               必须放在new Animal()这样的语句之后执行。<br>   2.无法实现多继承<br>   3.来自原型对象的所有属性被所有实例共享<br>   4.创建子类实例时，无法向父类构造函数传参</p>
</blockquote>
<h3 id="构造函数继承"><a href="#构造函数继承" class="headerlink" title="构造函数继承"></a>构造函数继承</h3><blockquote>
<p>使用父类的构造函数来增强子类实例，等于是复制父类的实例属性给子类（没用到原型）</p>
</blockquote>
<p><strong>父类：</strong></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 定义一个动物类</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Animal</span> (<span class="params">name</span>) </span>&#123;</span><br><span class="line">  <span class="comment">// 属性</span></span><br><span class="line">  <span class="keyword">this</span>.name = name || <span class="string">'Animal'</span>;</span><br><span class="line">  <span class="comment">// 实例方法</span></span><br><span class="line">  <span class="keyword">this</span>.sleep = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在睡觉！'</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 原型方法</span></span><br><span class="line">Animal.prototype.eat = <span class="function"><span class="keyword">function</span>(<span class="params">food</span>) </span>&#123;</span><br><span class="line">  <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在吃：'</span> + food);</span><br></pre></td></tr></table></figure>

<p><strong>子类：</strong></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Cat</span>(<span class="params">name</span>)</span>&#123;</span><br><span class="line">    Animal.call(<span class="keyword">this</span>);</span><br><span class="line">    <span class="keyword">this</span>.name= name || <span class="string">'Tom'</span>;</span><br><span class="line">&#125; </span><br><span class="line"></span><br><span class="line"><span class="comment">// Test Code</span></span><br><span class="line"><span class="keyword">var</span> cat = <span class="keyword">new</span> Cat();</span><br><span class="line"><span class="built_in">console</span>.log(cat.name);</span><br><span class="line"><span class="built_in">console</span>.log(cat.sleep());</span><br><span class="line"><span class="built_in">console</span>.log(cat <span class="keyword">instanceof</span> Animal);   <span class="comment">//false</span></span><br><span class="line"><span class="built_in">console</span>.log(cat <span class="keyword">instanceof</span> Cat); <span class="comment">// true</span></span><br></pre></td></tr></table></figure>

<p><strong>特点：</strong></p>
<blockquote>
<p>1.解决了1中，子类实例共享父类引用属性的问题<br> 2.创建子类实例时，可以向父类传递参数<br> 3.可以实现多继承（call多个父类对象）</p>
</blockquote>
<p><strong>缺点：</strong></p>
<blockquote>
<p>1.实例并不是父类的实例，只是子类的实例<br>   2.只能继承父类的实例属性和方法，不能继承原型属性/方法<br>   3.无法实现函数复用，每个子类都有父类实例函数的副本，影响性能</p>
</blockquote>
<h3 id="组合继承"><a href="#组合继承" class="headerlink" title="组合继承"></a>组合继承</h3><blockquote>
<p>通过调用父类构造，继承父类的属性并保留传参的优点，然后通过将父类实例作为子类原型，实现函数复用</p>
</blockquote>
<p><strong>父类：</strong></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 定义一个动物类</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Animal</span> (<span class="params">name</span>) </span>&#123;</span><br><span class="line">  <span class="comment">// 属性</span></span><br><span class="line">  <span class="keyword">this</span>.name = name || <span class="string">'Animal'</span>;</span><br><span class="line">  <span class="comment">// 实例方法</span></span><br><span class="line">  <span class="keyword">this</span>.sleep = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在睡觉！'</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 原型方法</span></span><br><span class="line">Animal.prototype.eat = <span class="function"><span class="keyword">function</span>(<span class="params">food</span>) </span>&#123;</span><br><span class="line">  <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在吃：'</span> + food);</span><br></pre></td></tr></table></figure>

<p><strong>子类：</strong></p>
<figure class="highlight stata"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line">function <span class="keyword">Cat</span>(name)&#123;</span><br><span class="line">  Animal.call(this);</span><br><span class="line">  this.name = name || 'Tom';</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">Cat</span>.prototype = new Animal();</span><br><span class="line"></span><br><span class="line"><span class="comment">//修复构造函数指向</span></span><br><span class="line"><span class="keyword">Cat</span>.prototype.constructor = <span class="keyword">Cat</span>;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">// Test Code</span></span><br><span class="line"><span class="keyword">var</span> <span class="keyword">cat</span> = new <span class="keyword">Cat</span>();</span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span>.name);</span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span>.<span class="keyword">sleep</span>());</span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span> instanceof Animal); <span class="comment">// true</span></span><br><span class="line">console.<span class="built_in">log</span>(<span class="keyword">cat</span> instanceof <span class="keyword">Cat</span>); <span class="comment">// true</span></span><br></pre></td></tr></table></figure>

<p><strong>特点：</strong></p>
<blockquote>
<p>1.弥补了方式2的缺陷，可以继承实例属性/方法，也可以继承原型属性/方法<br>   2.既是子类的实例，也是父类的实例<br>   3.不存在引用属性共享问题<br>   4.可传参,函数可复用</p>
</blockquote>
<p><strong>缺点：</strong></p>
<blockquote>
<p>调用了两次父类构造函数，生成了两份实例（子类实例将子类原型上的那份屏蔽了）</p>
</blockquote>
<h3 id="寄生组合继承"><a href="#寄生组合继承" class="headerlink" title="寄生组合继承"></a>寄生组合继承</h3><blockquote>
<p>通过寄生方式，砍掉父类的实例属性，这样，在调用两次父类的构造的时候，就不会初始化两次实例方法/属性，避免的组合继承的缺点</p>
</blockquote>
<p><strong>父类：</strong></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 定义一个动物类</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Animal</span> (<span class="params">name</span>) </span>&#123;</span><br><span class="line">  <span class="comment">// 属性</span></span><br><span class="line">  <span class="keyword">this</span>.name = name || <span class="string">'Animal'</span>;</span><br><span class="line">  <span class="comment">// 实例方法</span></span><br><span class="line">  <span class="keyword">this</span>.sleep = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在睡觉！'</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 原型方法</span></span><br><span class="line">Animal.prototype.eat = <span class="function"><span class="keyword">function</span>(<span class="params">food</span>) </span>&#123;</span><br><span class="line">  <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在吃：'</span> + food);</span><br></pre></td></tr></table></figure>

<p><strong>子类：</strong></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Cat</span>(<span class="params">name</span>)</span>&#123;</span><br><span class="line">  Animal.call(<span class="keyword">this</span>);</span><br><span class="line">  <span class="keyword">this</span>.name = name || <span class="string">'Tom'</span>;</span><br><span class="line">&#125;</span><br><span class="line">(<span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">  <span class="comment">// 创建一个没有实例方法的类</span></span><br><span class="line">  <span class="keyword">var</span> Super = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;&#125;;</span><br><span class="line">  Super.prototype = Animal.prototype;</span><br><span class="line">  <span class="comment">//将实例作为子类的原型</span></span><br><span class="line">  Cat.prototype = <span class="keyword">new</span> Super();</span><br><span class="line">&#125;)();</span><br><span class="line"></span><br><span class="line"><span class="comment">// Test Code</span></span><br><span class="line"><span class="keyword">var</span> cat = <span class="keyword">new</span> Cat();</span><br><span class="line"><span class="built_in">console</span>.log(cat.name);</span><br><span class="line"><span class="built_in">console</span>.log(cat.sleep());</span><br><span class="line"><span class="built_in">console</span>.log(cat <span class="keyword">instanceof</span> Animal); <span class="comment">// true</span></span><br><span class="line"><span class="built_in">console</span>.log(cat <span class="keyword">instanceof</span> Cat); <span class="comment">//true</span></span><br><span class="line"></span><br><span class="line">Cat.prototype.constructor = Cat; <span class="comment">// 需要修复下构造函数</span></span><br></pre></td></tr></table></figure>

<p><strong>或者：</strong></p>
<blockquote>
<p>继承实现的核心就是将父类的原型赋值给了子类，并且将构造函数设置为子类，这样既解决了无用的父类属性问题，还能正确的找到子类的构造函数。</p>
</blockquote>
<figure class="highlight typescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Cat</span>(<span class="params">name</span>)</span>&#123;</span><br><span class="line">  Animal.call(<span class="keyword">this</span>);</span><br><span class="line">  <span class="keyword">this</span>.name = name || <span class="string">'Tom'</span>;</span><br><span class="line">&#125;</span><br><span class="line"> </span><br><span class="line">Cat.prototype = <span class="built_in">Object</span>.create(Animal.prototype, &#123;</span><br><span class="line">  <span class="keyword">constructor</span>: &#123;</span><br><span class="line">    value: Cat,</span><br><span class="line">    enumerable: <span class="literal">false</span>,</span><br><span class="line">    writable: <span class="literal">true</span>,</span><br><span class="line">    configurable: <span class="literal">true</span></span><br><span class="line">  &#125;</span><br><span class="line">&#125;)</span><br><span class="line"> </span><br><span class="line"><span class="comment">// Test Code</span></span><br><span class="line"><span class="keyword">var</span> cat = <span class="keyword">new</span> Cat();</span><br><span class="line"><span class="built_in">console</span>.log(cat.name);</span><br><span class="line"><span class="built_in">console</span>.log(cat.sleep());</span><br><span class="line"><span class="built_in">console</span>.log(cat <span class="keyword">instanceof</span> Animal); <span class="comment">// true</span></span><br><span class="line"><span class="built_in">console</span>.log(cat <span class="keyword">instanceof</span> Cat); <span class="comment">//true</span></span><br></pre></td></tr></table></figure>

<p><strong>特点：</strong></p>
<blockquote>
<p>堪称完美</p>
</blockquote>
<p><strong>缺点：</strong></p>
<blockquote>
<p>实现较为复杂</p>
</blockquote>
<h3 id="Class-继承"><a href="#Class-继承" class="headerlink" title="Class 继承"></a>Class 继承</h3><blockquote>
<p>在 ES6 中，我们可以使用 class 去实现继承，并且实现起来很简单,使用 extends 表明继承自哪个父类，并且在子类构造函数中必须调用 super，这段代码可以看成 Animal.call(this, name)。Class 的本质就是函数</p>
</blockquote>
<p><strong>父类：</strong></p>
<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 定义一个动物类</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">Animal</span> (<span class="params">name</span>) </span>&#123;</span><br><span class="line">  <span class="comment">// 属性</span></span><br><span class="line">  <span class="keyword">this</span>.name = name || <span class="string">'Animal'</span>;</span><br><span class="line">  <span class="comment">// 实例方法</span></span><br><span class="line">  <span class="keyword">this</span>.sleep = <span class="function"><span class="keyword">function</span>(<span class="params"></span>)</span>&#123;</span><br><span class="line">    <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在睡觉！'</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 原型方法</span></span><br><span class="line">Animal.prototype.eat = <span class="function"><span class="keyword">function</span>(<span class="params">food</span>) </span>&#123;</span><br><span class="line">  <span class="built_in">console</span>.log(<span class="keyword">this</span>.name + <span class="string">'正在吃：'</span> + food);</span><br></pre></td></tr></table></figure>

<p><strong>子类：</strong></p>
<figure class="highlight scala"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Cat</span> <span class="keyword">extends</span> <span class="title">Animal</span> </span>&#123;</span><br><span class="line">    constructor(name)&#123;</span><br><span class="line">　　　　<span class="keyword">super</span>(name);&lt;br&gt;　　　　<span class="keyword">this</span>.name= name || <span class="symbol">'Anima</span>l';</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> cat = <span class="keyword">new</span> <span class="type">Cat</span>();</span><br><span class="line">console.log(cat.name);</span><br><span class="line">console.log(cat.sleep());</span><br><span class="line">console.log(cat instanceof <span class="type">Animal</span>); <span class="comment">// true</span></span><br><span class="line">console.log(cat instanceof <span class="type">Cat</span>); <span class="comment">//true</span></span><br></pre></td></tr></table></figure>
      
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        <div style="text-align:center;color: #ccc;font-size:14px;">-------------本文结束<i class="fa fa-paw"></i>感谢您的阅读-------------</div>
    
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  <script type="text/javascript">
    // Popup Window;
    var isfetched = false;
    var isXml = true;
    // Search DB path;
    var search_path = "search.xml";
    if (search_path.length === 0) {
      search_path = "search.xml";
    } else if (/json$/i.test(search_path)) {
      isXml = false;
    }
    var path = "/" + search_path;
    // monitor main search box;

    var onPopupClose = function (e) {
      $('.popup').hide();
      $('#local-search-input').val('');
      $('.search-result-list').remove();
      $('#no-result').remove();
      $(".local-search-pop-overlay").remove();
      $('body').css('overflow', '');
    }

    function proceedsearch() {
      $("body")
        .append('<div class="search-popup-overlay local-search-pop-overlay"></div>')
        .css('overflow', 'hidden');
      $('.search-popup-overlay').click(onPopupClose);
      $('.popup').toggle();
      var $localSearchInput = $('#local-search-input');
      $localSearchInput.attr("autocapitalize", "none");
      $localSearchInput.attr("autocorrect", "off");
      $localSearchInput.focus();
    }

    // search function;
    var searchFunc = function(path, search_id, content_id) {
      'use strict';

      // start loading animation
      $("body")
        .append('<div class="search-popup-overlay local-search-pop-overlay">' +
          '<div id="search-loading-icon">' +
          '<i class="fa fa-spinner fa-pulse fa-5x fa-fw"></i>' +
          '</div>' +
          '</div>')
        .css('overflow', 'hidden');
      $("#search-loading-icon").css('margin', '20% auto 0 auto').css('text-align', 'center');

      $.ajax({
        url: path,
        dataType: isXml ? "xml" : "json",
        async: true,
        success: function(res) {
          // get the contents from search data
          isfetched = true;
          $('.popup').detach().appendTo('.header-inner');
          var datas = isXml ? $("entry", res).map(function() {
            return {
              title: $("title", this).text(),
              content: $("content",this).text(),
              url: $("url" , this).text()
            };
          }).get() : res;
          var input = document.getElementById(search_id);
          var resultContent = document.getElementById(content_id);
          var inputEventFunction = function() {
            var searchText = input.value.trim().toLowerCase();
            var keywords = searchText.split(/[\s\-]+/);
            if (keywords.length > 1) {
              keywords.push(searchText);
            }
            var resultItems = [];
            if (searchText.length > 0) {
              // perform local searching
              datas.forEach(function(data) {
                var isMatch = false;
                var hitCount = 0;
                var searchTextCount = 0;
                var title = data.title.trim();
                var titleInLowerCase = title.toLowerCase();
                var content = data.content.trim().replace(/<[^>]+>/g,"");
                var contentInLowerCase = content.toLowerCase();
                var articleUrl = decodeURIComponent(data.url);
                var indexOfTitle = [];
                var indexOfContent = [];
                // only match articles with not empty titles
                if(title != '') {
                  keywords.forEach(function(keyword) {
                    function getIndexByWord(word, text, caseSensitive) {
                      var wordLen = word.length;
                      if (wordLen === 0) {
                        return [];
                      }
                      var startPosition = 0, position = [], index = [];
                      if (!caseSensitive) {
                        text = text.toLowerCase();
                        word = word.toLowerCase();
                      }
                      while ((position = text.indexOf(word, startPosition)) > -1) {
                        index.push({position: position, word: word});
                        startPosition = position + wordLen;
                      }
                      return index;
                    }

                    indexOfTitle = indexOfTitle.concat(getIndexByWord(keyword, titleInLowerCase, false));
                    indexOfContent = indexOfContent.concat(getIndexByWord(keyword, contentInLowerCase, false));
                  });
                  if (indexOfTitle.length > 0 || indexOfContent.length > 0) {
                    isMatch = true;
                    hitCount = indexOfTitle.length + indexOfContent.length;
                  }
                }

                // show search results

                if (isMatch) {
                  // sort index by position of keyword

                  [indexOfTitle, indexOfContent].forEach(function (index) {
                    index.sort(function (itemLeft, itemRight) {
                      if (itemRight.position !== itemLeft.position) {
                        return itemRight.position - itemLeft.position;
                      } else {
                        return itemLeft.word.length - itemRight.word.length;
                      }
                    });
                  });

                  // merge hits into slices

                  function mergeIntoSlice(text, start, end, index) {
                    var item = index[index.length - 1];
                    var position = item.position;
                    var word = item.word;
                    var hits = [];
                    var searchTextCountInSlice = 0;
                    while (position + word.length <= end && index.length != 0) {
                      if (word === searchText) {
                        searchTextCountInSlice++;
                      }
                      hits.push({position: position, length: word.length});
                      var wordEnd = position + word.length;

                      // move to next position of hit

                      index.pop();
                      while (index.length != 0) {
                        item = index[index.length - 1];
                        position = item.position;
                        word = item.word;
                        if (wordEnd > position) {
                          index.pop();
                        } else {
                          break;
                        }
                      }
                    }
                    searchTextCount += searchTextCountInSlice;
                    return {
                      hits: hits,
                      start: start,
                      end: end,
                      searchTextCount: searchTextCountInSlice
                    };
                  }

                  var slicesOfTitle = [];
                  if (indexOfTitle.length != 0) {
                    slicesOfTitle.push(mergeIntoSlice(title, 0, title.length, indexOfTitle));
                  }

                  var slicesOfContent = [];
                  while (indexOfContent.length != 0) {
                    var item = indexOfContent[indexOfContent.length - 1];
                    var position = item.position;
                    var word = item.word;
                    // cut out 100 characters
                    var start = position - 20;
                    var end = position + 80;
                    if(start < 0){
                      start = 0;
                    }
                    if (end < position + word.length) {
                      end = position + word.length;
                    }
                    if(end > content.length){
                      end = content.length;
                    }
                    slicesOfContent.push(mergeIntoSlice(content, start, end, indexOfContent));
                  }

                  // sort slices in content by search text's count and hits' count

                  slicesOfContent.sort(function (sliceLeft, sliceRight) {
                    if (sliceLeft.searchTextCount !== sliceRight.searchTextCount) {
                      return sliceRight.searchTextCount - sliceLeft.searchTextCount;
                    } else if (sliceLeft.hits.length !== sliceRight.hits.length) {
                      return sliceRight.hits.length - sliceLeft.hits.length;
                    } else {
                      return sliceLeft.start - sliceRight.start;
                    }
                  });

                  // select top N slices in content

                  var upperBound = parseInt('1');
                  if (upperBound >= 0) {
                    slicesOfContent = slicesOfContent.slice(0, upperBound);
                  }

                  // highlight title and content

                  function highlightKeyword(text, slice) {
                    var result = '';
                    var prevEnd = slice.start;
                    slice.hits.forEach(function (hit) {
                      result += text.substring(prevEnd, hit.position);
                      var end = hit.position + hit.length;
                      result += '<b class="search-keyword">' + text.substring(hit.position, end) + '</b>';
                      prevEnd = end;
                    });
                    result += text.substring(prevEnd, slice.end);
                    return result;
                  }

                  var resultItem = '';

                  if (slicesOfTitle.length != 0) {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + highlightKeyword(title, slicesOfTitle[0]) + "</a>";
                  } else {
                    resultItem += "<li><a href='" + articleUrl + "' class='search-result-title'>" + title + "</a>";
                  }

                  slicesOfContent.forEach(function (slice) {
                    resultItem += "<a href='" + articleUrl + "'>" +
                      "<p class=\"search-result\">" + highlightKeyword(content, slice) +
                      "...</p>" + "</a>";
                  });

                  resultItem += "</li>";
                  resultItems.push({
                    item: resultItem,
                    searchTextCount: searchTextCount,
                    hitCount: hitCount,
                    id: resultItems.length
                  });
                }
              })
            };
            if (keywords.length === 1 && keywords[0] === "") {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-search fa-5x" /></div>'
            } else if (resultItems.length === 0) {
              resultContent.innerHTML = '<div id="no-result"><i class="fa fa-frown-o fa-5x" /></div>'
            } else {
              resultItems.sort(function (resultLeft, resultRight) {
                if (resultLeft.searchTextCount !== resultRight.searchTextCount) {
                  return resultRight.searchTextCount - resultLeft.searchTextCount;
                } else if (resultLeft.hitCount !== resultRight.hitCount) {
                  return resultRight.hitCount - resultLeft.hitCount;
                } else {
                  return resultRight.id - resultLeft.id;
                }
              });
              var searchResultList = '<ul class=\"search-result-list\">';
              resultItems.forEach(function (result) {
                searchResultList += result.item;
              })
              searchResultList += "</ul>";
              resultContent.innerHTML = searchResultList;
            }
          }

          if ('auto' === 'auto') {
            input.addEventListener('input', inputEventFunction);
          } else {
            $('.search-icon').click(inputEventFunction);
            input.addEventListener('keypress', function (event) {
              if (event.keyCode === 13) {
                inputEventFunction();
              }
            });
          }

          // remove loading animation
          $(".local-search-pop-overlay").remove();
          $('body').css('overflow', '');

          proceedsearch();
        }
      });
    }

    // handle and trigger popup window;
    $('.popup-trigger').click(function(e) {
      e.stopPropagation();
      if (isfetched === false) {
        searchFunc(path, 'local-search-input', 'local-search-result');
      } else {
        proceedsearch();
      };
    });

    $('.popup-btn-close').click(onPopupClose);
    $('.popup').click(function(e){
      e.stopPropagation();
    });
    $(document).on('keyup', function (event) {
      var shouldDismissSearchPopup = event.which === 27 &&
        $('.search-popup').is(':visible');
      if (shouldDismissSearchPopup) {
        onPopupClose();
      }
    });
  </script>





  

  

  

  
  

  

  

  


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